Mountings for attachment between a supporting member and a supported member which use a combination of fluid and elastomer have been proposed in a variety of applications including on aircraft, automobiles, boats and for supporting many types of engines. The elastomer, typically natural rubber, provides the stiffness needed for static support of the supported member. The fluid, typically glycol or silicone, provides i) excellent vibration isolation by tuning the fluid mass, or ii) damping by throttling the fluid, or iii) combinations thereof.
U.S. Pat. No. 4,236,607 hereby incorporated by reference, describes a fluid mounting or vibration isolator which uses a tuned fluid, specifically mercury, to generate amplified counter-inertial forces. Although the isolator performed acceptably, mercury has the disadvantages that it is toxic and very corrosive.
The commonly assigned Jones U.S. Pat. No. 4,811,919 hereby incorporated by reference, describes a volume compensated fluid mounting of the double-pumping or double-acting variety, including a volume compensator of the air-charged type. The air-charged compensator is used to accommodate the displaced fluid volume due to exposing the mounting to elevated temperatures. This type of mounting is particularly useful for attaching an aircraft engine to an aircraft strut at the front mounting location where the environment is comparatively cool (about 150 deg F.). Although adequate for the cooler front mount application, the Jones '919 mounting would be inadequate for most aft mount applications, where the temperature generally will exceed 200 deg F., and may exceed 300 deg F. The Jones '919 mounting has the disadvantage that, as it is exposed to high-temperature environments, it will build up edge induced compression strains (ENT's) or bulge strains in the elastomeric elements 35 and 36. This is because the elastomeric elements 35 and 36 are constrained or fixed between a frame 20 and a support member 30 which includes flanges 31 and 32. This type of mounting will be referred to as a constrained-type mounting. As the elevated temperatures cause the elastomeric elements 35 and 36 to heat up, bulge strains will build up at the surface of the elastomeric elements 35 and 36. These bulge strains alone, at very elevated temperatures can be enough to rupture the bond on this type of mounting. More commonly, these high bulge strains due to temperature, in combination with the high bulge strains due to operating loads imparted to the mountings, will cause damage to the elastomer sections 35 and 36.
Furthermore, these constrained-type mountings need to be molded at high pressures to ensure that none of the elastomer sections 35 and 36 are placed in tension while under the application of load. In essence, the high-pressure bonding provides pre-compression to the elastomer sections. As is known to those skilled in the art, placing a laminated section in tension is undesirable because cavitation in the elastomer that may occur. High-pressure bonding requires special bonding procedures and molds and adds undesirable complexity to the mold and processing of the mounting.
Fluid mountings which use an air-charged compensator have a further disadvantage in that they require a large envelope to house the compensator assembly, when employed in high-temperature applications. Typically, greater than five times the expansion volume of the fluid is required for proper sizing of an air-charged compensator to ensure that high pressures do not build up within the mounting and air-charged compensator. This is true for two reasons. One, not only is the mounting exposed to elevated temperature, but so too, is the air chamber within the air-charged compensator. Consequently, the air-charged compensator will also build up high pressures within it. Therefore, in order to minimize the pressure increase, the volume of the air chamber within the air-charged compensator is made large. Secondly, as the fluid in the mounting expands into the fluid expansion chamber, the volume of air in the air chamber decreases proportionately, and the pressure in the air-charged compensator, and thus the mounting, increases. Again, in order to minimize this pressure increase, the volume within the air chamber is made large.
Co-pending application Ser. No. 07/706,622 filed on May 29, 1991 entitled "Adaptive Fluid Mount" describes a fluid mounting which utilizes an air-charged compensator and constrained-type elastomer sections. This type of fluid mounting is particularly useful for front engine mount applications where the temperature environment is comparatively cool. The mounting is adjustable in that the lengths and diameters of the inertia tracks differ to provide tunability without having to rebond the mounting. However, the amount of tuning available is limited, since the inertia term alone will allow one to tune the mounting only so far. Alternatively, tuning could be accomplished by tearing the mount apart to effect a change in the volume stiffness requiring rebonding the entire mounting. However, this is a very expensive proposition.
In addition to the aforementioned problems of the related mountings, the currently known elastomer-and-fluid combinations used in fluid mountings will tend to degrade and break down the elastomer section, over time, when they are exposed to elevated temperature environments. The degradation process will include fluid migrating into the elastomer sections, swelling them, and lessening their tensile strengths. Further, fillers and other ingredients within the elastomer sections will leach into the fluid and contaminate it, and may change its viscosity which can impact the fluid mount's performance.
Previous fluid mountings have used combinations of natural rubber elastomers and silicone or glycol fluids. Natural rubber elastomers are chosen particularly for their strength and resiliency for use in mountings, and particularly for use in dampers and isolators. Glycol and silicone fluids are used for their low cost and inert properties. However, the combination of natural rubber and glycol or silicone fluids is generally limited in operation, for extended periods, to temperatures less than about 200 deg F. If this combination is used in environments which see temperatures in excess of 200 deg F. for extended periods, conventional fluids, such as glycol or silicone fluids, will aggressively attack the elastomer and may attack the bond formed at the elastomer/metal interface, as well. Continued exposure to elevated temperatures will, eventually, cause the elastomer to revert and become gummy in consistency. These elevated temperature environments, generally encountered in aircraft applications, and especially aft mount applications, require a fluid and elastomer combination which will be compatible at elevated temperatures over extended periods of time.
Co-pending application Ser. No. 07/514,071 now U.S. Pat. No. 5,108,045 filed on Apr. 25, 1990 entitled "Engine Mounting Assembly" describes an engine mounting which provides for the elastomer sections to be loaded in pure shear or pure compression, thus leading to enhanced service life, and linearity. This type of engine mounting is particularly useful for aft engine mount situations where the temperatures are severe.